1. Field of the Invention
The present invention relates generally to an improved push-in interbody (for placement at least in part between adjacent vertebral bodies in the space previously occupied by disc material) spinal fusion implant for the immobilization of vertebrae. The present invention is directed to expandable push-in implants only not including push-in implants having substantially arcuate upper and lower members oriented toward the adjacent vertebral bodies and designed to engage the vertebral bodies along arcuate cuts therein typically formed by a drill. Further, the present invention is not directed to threaded implants requiring rotation for insertion into the implantation space in the spine. In particular, the invention relates to push-in spinal fusion implants that have height raising capabilities that are utilized once the implant is initially positioned. Such height raising capability may be utilized within the spine anteriorly, posteriorly, or both and to various extents, respectively so as to raise the front, back, or both of the implant by the same or various amounts. More particularly, the invention relates to a push-in implant having upper and lower surfaces of upper and lower members that in a first or insertion position are collapsed relative to one another and in a second or deployed position are adapted to contact the adjacent vertebral bodies.
2. Description of the Related Art
Push-in spinal fusion implants having upper and lower surfaces adapted for placement in contact with adjacent vertebral bodies are known in the related art. Such a push-in spinal fusion implant was invented by Michelson and is disclosed in U.S. Pat. No. 5,776,199, filed Jun. 28, 1988, which is hereby incorporated by reference.
Lordotic or tapered, push-in spinal fusion implants are also known in the art. By way of example, Michelson has invented such implants as disclosed in U.S. Pat. No. 5,609,635, filed Jun. 7, 1995, which is hereby incorporated by reference.
Expandable fusion implants are known in the related art. The first expandable spinal fusion (allowing for the growth of bone from vertebral body to vertebral body through the implant) implant was invented by Michelson and also is disclosed in U.S. Pat. No. 5,776,199 previously incorporated by reference herein.
Lordotic or tapered, spinal fusion implants have the advantage of restoring or enhancing spinal lordosis. Push-in spinal fusion implants offer the advantage of being easily positioned in the implantation space and of having excellent fastening or holding features. Expandable fusion implants offer the advantage of allowing for the placement of a potentially larger implant through a smaller opening in a patient's body. Selective expansion along a single direction, (e.g. vertically only when correctly installed) offers the advantage of increasing the height of the implant and therefore the distraction of the disc space, but without a concomitant increase in the width of the implant.
There exists a need for an artificial interbody spinal fusion implant providing for all of the aforementioned advantages in combination.